Although sites and sounds, as they exist in nature, are analog, the advantages of recording and storing them in a digital format have been known for years. A digitally recorded image or sound is stored on digital media as a series of 1's and 0's. When reproduced, an exact copy of the original recording is obtained. The clarity of the digital recording can be immediately appreciated.
One of the first types of digital media introduced to the consumer market was the compact disk (CD), which replaced vinyl records and tapes. Since then, many other types of digital media, such as digital tapes, DVDs, Flash memory devices, and others have been introduced and are in widespread use. Because the digital recordings are only values of 1's and 0's, in stark contrast to the previously-used analog method of recording, all generations of copies of a digital recording have the same quality as the original.
To display analog video, a scanning device systematically and continuously moves across the screen placing a portion of the image to be displayed at each address, or “pixel.” A magnetic field is used to direct the electrons to that address. The scanning occurs so rapidly that the human eye cannot detect that the entire picture is not displayed at once. Because the scanning device is responsible for displaying every pixel in an image, if the single scanning device would fail, no image would display and the display unit would be rendered worthless.
Very recently, several new technologies have emerged that allow digital video to be displayed. At the forefront is a projection display technology called Digital Light Processing™ (DLP™). DLP televisions and projectors utilizing matrices of 800 to over a million “microelectromechanical systems” (MEMS) devices known as Digital Micromirror Devices (DMDs). A DMD is a fast, reflective, digital light switch.
Referring to FIG. 1, a DMD 100 is shown. The DMD includes a mirror 102 located above and attached to a semiconductor chip 104 by a post 106. The mirror 102 and post 106 rest on a yoke 108 supported by a hinge 110. The yoke 108 is attached to a center of the hinge 110 and each of two ends of the hinge 110 is terminated into a hinge support 120.
On opposite longitudinal sides of the hinge 110 are electrodes 112 and 114. Each electrode 112 and 114 is attached to an individual address pad 116 and 118, respectively, by electrode support posts 122 and 124, respectively. The hinge supports 120 are supported by a bias/reset bus 126 and are attached by a pair of hinge support posts 128.
When stimulated by a voltage generated from either of the electrodes 112 or 114, the yoke 108 and mirror 102 pivot along the hinge 110. The limits of the pivot motion are defined by contact points where the yoke 108 makes contact with landing sites 130 on the bias/reset bus 126 surface. Typically, the mirror pivots a total of about 20°.
All images on a screen are actually made of a matrix of small “pixels.” In DLP devices, each mirror corresponds to an individual pixel on the screen. If the mirror reflects light onto its assigned pixel, the pixel becomes energized and is illuminated.
More specifically, each DMD is addressable and completely independent of the other DMDs. A processor directs applied voltages to the electrodes 112 and 114 so as to cause each DMD to pivot in a desired direction. By pivoting a mirror from one contact point 118 to the other 116, light for a pixel of an image can be directed to one of two places: a display screen or a light absorbing area. Referring now to FIG. 2, it can be seen that when light is directed from a source 302 to one or more of the mirrors 102 in a first position 204, that light is reflected to a display screen 324 in a location corresponding to the mirror's position within the array of mirrors. When one or more of the mirrors 102 is in a second position 210, the light is reflected to a second location, such as a light absorbing area 322. By varying the mirrors 102 between the two positions, each mirror 102 operates as a digital on/off light switch.
To place an image on the screen of a DLP device, the image is separated into its red, blue, and green components and digitized into a large number of samples (for example, 1,310,000 samples) for each color. Each mirror in the DLP system is assigned one of these samples. A color wheel is placed between a light source and the DMD. The color wheel continuously rotates between the primary colors so that each color is serially projected onto the DMD mirrors. By switching on and off, the DMDs determine which pixels on the screen receive each color. Amazingly, a DMD mirror is capable of switching thousands of times per second. Varying the duty cycle, or amount of time each individual DMD mirror is on, allows over 16 million different colors to be displayed from the single light source and primary color wheel.
Because there are a very large number of moving micromirrors that are each separated by only a small distance (for example, only 1 μm) on a DMD chip, DLP devices suffer from the disadvantage that manufacturing is difficult and results in a great number of defective chips. Even the smallest contaminate, such as dust or moisture, can prevent one or more mirrors from operating properly. Additionally, because of the extraordinarily large number of movements required in the life of each DMD switch, failures of individual switches in the DLP matrix can be expected.
In a DLP device, if one of the DMD mirrors is defective, its corresponding pixel on the screen will show a “dead,” or black, spot if the mirror is stuck in the “off” position.